A wide variety of implantable infusion devices are available for delivering fluid to target locations of patients into which the devices are implanted. Available and proposed devices can differ in their ability to control the flow rate of fluid delivered from the device to the patient. For example, Medtronic Inc.'s (Minneapolis, Minn.) SYNCHROMED series of implantable infusion devices are programmable devices where the flow rate may be varied according to instructions provided by, e.g., a physician programmer device. Programmable implantable infusion devices can provide a wide range of fluid flow rates and are typically designed to deliver small amounts of therapeutic agent over time.
Such devices have been used successfully to treat a variety of diseases. However, in some patients it may be desirable to deliver a bolus infusion of therapeutic agent that exceeds the amount deliverable by existing programmable infusion devices. For example, it may be desirable to deliver 1 milliliter or more in a minute. While devices that can accomplish such infusion rates are theoretically possible, such devices may suffer certain safety drawbacks, such as MRI safety.
When a patient having an implanted infusion device is subjected to an MRI procedure, the magnetic field may result in unpredictable opening or closing of valves in the infusion device. If a device capable of delivering a high infusion rate requires a valve to control the delivery of therapeutic agent, unpredictable opening of the valve during an MRI procedure may result in an undesired or unsafe amount of therapeutic agent to be delivered to the patient during the MRI procedure.